ball crossing third base

[Dakota]

It is not possible for a ball to cross or bound over a base on a properly laid out field and be in foul territory. The base is entirely in fair territory.

For crossing over the base to be a factor, the ball must be bounding (i.e. have already hit the ground). Where it hit the ground (fair or foul territory) is irrelevant, so long as it has not yet passed 1st or 3rd base.

If the bounding ball crosses over the base, it is fair.